1. Field of the Invention
The present invention relates to a coating method of a coating solution, and particularly relates to a coating method of a coating solution for performing ultra thin film coating of a coating solution with low viscosity by using a slot die.
2. Description of the Related Art
In a coating method for coating a coating solution onto a web while being supported by a backup roller by using a slot die having a decompression chamber, stepped unevenness where film thickness of the coating film has stepped unevenness in a traveling direction of a web occurs due to disturbance elements such as feeding unevenness of the web, decompression variation, pulsation at the time of delivery of the coating solution, pulsation of the slot die and the backup roller, flatness of the web (degree of irregularities) and the like.
Incidentally, high functional thin-layer films for antireflection, glare protection, enlargement of a view angle and the like which are used in a liquid crystal display and the like are manufactured by coating a web with a coating solution having these functions. In order to allow the high functional thin-layer film to exhibit desired functions with high accuracy, in recent years, it is required to coat an ultra-thin film (for example, wet film thickness of 10 μm or less) with low viscosity (for example, 0.005 Pa·s or lower) as compared with the conventional coating solution. Since a leveling effect of the coating solution after coated cannot be expected in the case of low viscosity/ultra-thin film coating, it becomes important how the stepped unevenness is suppressed during coating. For this reason, improvement has been made for suppression of the above described disturbances themselves and a bead shape having high resistance against the disturbances.
As for the conventional measures for suppression of stepped unevenness, it is proposed to set the decompression degree at −200 to −300 Pa in Japanese Patent Application Laid-Open No. 2003-285343. Besides, in National Publication of International Patent Application No. 9-511682 and Japanese Patent Application Laid-Open No. 2003-211052, it is proposed to contour a lip tip end of a slot die into an overbite shape. Besides, in Japanese Patent Application Laid-Open No. 2003-236434, it is proposed to increase a clearance of side/back plates to relieve variation of the decompression degree in the decompression chamber.